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PubMed1995

Pineal opsin: a nonvisual opsin expressed in chick pineal.

Pineal opsin (P-opsin), an opsin from chick that is highly expressed in pineal but is not detectable in retina, was cloned by the polymerase chain reaction. It is likely that the P-opsin lineage diverged from the retinal opsins early in opsin evolution. The amino acid sequence of P-opsin is 42 to 46 percent identical to that of the retinal opsins. P-opsin is a seven-membrane spanning, G protein-linked receptor with a Schiff-base lysine in the seventh membrane span and a Schiff-base counterion in the third membrane span. The primary sequence of P-opsin suggests that it will be maximally sensitive to approximately 500-nanometer light and produce a slow and prolonged phototransduction response consistent with the nonvisual function of pineal photoreception.

Amino Acid Sequence↗
PubMed2006

Remodeling of the cone photoreceptor mosaic during metamorphosis of flounder (Pseudopleuronectes americanus).

The retinal cone mosaic of the winter flounder, Pseudopleuronectes americanus, is extensively remodeled during metamorphosis when its visual system shifts from monochromatic to trichromatic. Here we describe the reorganization and re-specification of existing cone subtypes in which larval cones alter their spatial arrangement, morphology, and opsin expression to determine whether mechanisms controlling cell birth, mosaic position, and opsin selection are coordinated or independent. We labeled dividing cells with tritiated ((3)H) thymidine prior to mosaic remodeling to determine whether existing cone photoreceptors change phenotype. We also used in situ hybridization to identify mosaic type and opsin expression in transitional retinas to understand the sequence of transformation. Our data indicate that in the winter flounder retina the choice of new opsin species and the cellular rearrangement of the mosaic proceed independently. The production of the precise cone mosaic arrangement is not due to a stereotyped series of sequential cellular inductions, but rather might be the product of a set of distinct, flexible processes that rely on plasticity in cell phenotype.

Alkaline Phosphatase↗
PubMed2001

The relationship between opsin overexpression and photoreceptor degeneration.

PURPOSE: To characterize the process by which overexpression of normal opsin leads to photoreceptor degeneration. METHODS: Three transgenic mouse lines were generated that express different levels of an opsin with three amino acid modifications at the C terminus. These modifications created an epitopic site that can be readily distinguished from the endogenous protein using a bovine opsin-specific antibody. Evidence of degeneration associated with opsin overexpression was provided by anatomic studies and electroretinogram (ERG) recordings. Western blot analysis was used to confirm the production of the transgenic opsin, and an enzyme-linked immunosorbent assay (ELISA) was used to determine the amounts of opsin overexpressed in each line. Immunocytochemistry was used to determine the cellular localization of transgenic opsin. Amounts of 11-cis retinal were determined by extraction and high-performance liquid chromatography (HPLC). RESULTS: Opsin expression levels in the three lines were found to be 123%, 169%, and 222% of the level measured in nontransgenic animals, providing direct correlation between the level of transgene expression and the severity of the degenerative phenotype. In the lower expressing lines, ERG a-wave amplitudes were reduced to less than approximately 30% and 15% of normal values, whereas responses of the highest expressing line were indistinguishable from noise. In the lowest expressor, a 26% elevation in 11-cis retinal was observed, whereas in the medium and the high expressors, 11-cis retinal levels were increased by only 30% to 33%, well below the 69% and 122% increases in opsin levels. CONCLUSIONS: The overexpression of normal opsin induces photoreceptor degeneration that is similar to that seen in many mouse models of retinitis pigmentosa. This degeneration can be induced by opsin levels that exceed by only approximately 23% that of the normal mouse retina. Opsin overexpression has potential implications in retinitis pigmentosa.

Amino Acid Sequence↗
PubMed1995

Retinoid cycling proteins redistribute in light-/dark-adapted octopus retinas.

In cephalopods, the complex rhodopsin-retinochrome system serves to regenerate metarhodopsin and metaretinochrome after illumination. In the dark, a soluble protein, retinal-binding protein (RALBP), shuttles 11-cis retinal released from metaretinochrome located in the photoreceptor inner segments to metarhodopsin present in the rhabdoms. While in the rhabdoms, RALBP delivers 11-cis retinal to regenerate rhodopsin and in turn binds the all-trans isomer released by metarhodopsin. RALBP then returns all-trans retinal to the inner segments to restore retinochrome. The conventional interpretation of retinoid cycling is contradicted by immunocytochemical studies showing that, in addition to rhodopsin, retinochrome is present in the rhabdomal compartment, making possible the direct exchange of chromophores between the metapigments with the potential exclusion of RALBP. By using immunofluorescence and laser scanning confocal microscopy, we have precisely located opsin, aporetinochrome, and RALBP in light-/dark-adapted octopus retinas. We found differences in the distribution of all three proteins throughout the retina. Most significantly, comparison of cross sections though light- and dark-adapted rhabdoms showed a dramatic shift in position of the proteins. In the dark, opsin and retinochrome colocalized at the base of the rhabdomal microvilli. In the light, opsin redistributed along the length of the microvillar membranes, and retinochrome retreated to a location that is perhaps extracellular. RALBP was present in the core cytoplasm of the photoreceptor outer segments in the dark, and RALBP moved to the periphery in the light. Because of the colocalization of opsin and retinochrome in the dark, we believe that the two metapigments participate directly in chromophore exchange. RALBP may serve to transport additional chromophore from the inner segments to the rhabdoms and may not be immediately involved in the exchange process.

Adaptation, Ocular↗
PubMed1998

A perspective on color vision in platyrrhine monkeys.

Studies carried out over the past two decades show that many platyrrhine (New World) monkeys have polymorphic color vision. This condition results from the sorting of allelic versions of X-chromosome cone opsin genes at a single gene site, yielding a mixture of dichromatic and trichromatic phenotypes in the population. Two genera of platyrrhine monkey are known to deviate significantly from this pattern. Examination of color vision, photopigments, and photopigment genes of all of these monkeys have stimulated a renewed interest in understanding the evolution of primate color vision.

Animals↗
PubMed2000

Genetic evidence for selective transport of opsin and arrestin by kinesin-II in mammalian photoreceptors.

To test whether kinesin-II is important for transport in the mammalian photoreceptor cilium, and to identify its potential cargoes, we used Cre-loxP mutagenesis to remove the kinesin-II subunit, KIF3A, specifically from photoreceptors. Complete loss of KIF3A caused large accumulations of opsin, arrestin, and membranes within the photoreceptor inner segment, while the localization of alpha-transducin was unaffected. Other membrane, organelle, and transport markers, as well as opsin processing appeared normal. Loss of KIF3A ultimately caused apoptotic photoreceptor cell death similar to a known opsin transport mutant. The data suggest that kinesin-II is required to transport opsin and arrestin from the inner to the outer segment and that blocks in this transport pathway lead to photoreceptor cell death as found in retinitis pigmentosa.

Animals↗
PubMed2003

Development of the cone photoreceptor mosaic in the mouse retina revealed by fluorescent cones in transgenic mice.

PURPOSE: Normal function of the retina relies on the orderly stereotyped organization of different neurons and their synaptic connections. How such neural organization is patterned during development remains poorly understood due to the paucity of adequate developmental markers. This study was to examine the spatial organization and development of cone photoreceptors quantitatively in the mouse retina. METHODS: A transgenic approach was used to generate a living cone cell marker by driving GFP expression in mouse cones with the human red/green opsin gene 5' sequences. The spatial organization and development of the cones in the mouse retinas were examined quantitatively with epifluorescence and scanning laser confocal microscopy. Cone specific GFP expression in the developing retinas was verified with peanut agglutinin (PNA) staining. Developmental expression of mouse cone opsin genes was determined with RT-PCR. RESULTS: The fluorescent retinal cells expressing GFP can be visualized as early as on embryonic day E15. Following up morphological differentiation of these cells revealed features that were consistent with the typical morphology of the mouse cones. Double labeling with cone specific PNA showed that these cells were co-labeled starting from postnatal day P1, and that a subpopulation of PNA positive cones expressed the GFP. The fluorescent cell densities had a similar ventral and dorsal distribution from E15 to P2, increased dramatically in the ventral by P6, and in the dorsal from P7. Nearest neighbor distance analysis demonstrated that this subpopulation of cones was organized into a regular mosaic pattern with a regularity index of 4.82 in the central and 3.55 in the peripheral retina. Quantitative pattern assessment of the developing cones revealed that the fluorescent cells appeared to be distributed in a non-random array before birth. The regularity of the cone array began to rise on P7, in parallel with the onset of mouse green opsin gene expression and the development of cone pedicles. The regular pattern of cone mosaic organization was basically formed by P10, coinciding with the timing of the cone pedicle maturation. CONCLUSIONS: The cones in the mouse retina are organized in a regular mosaic pattern. Patterning the cone mosaic appears to follow a two phase developmental process involving regulated opsin gene expression and cone pedicle maturation: an early phase where a non-random array emerges during cone differentiation, and a late phase where the regular mosaic pattern is mature at the time when cone synaptic contacts are being formed.

Animals↗
PubMed1987

An opsin gene that is expressed only in the R7 photoreceptor cell of Drosophila.

We have used two techniques to isolate and characterize eye-specific genes from Drosophila melanogaster. First, we identified genes whose expression is limited to eyes, photoreceptor cells, or R7 photoreceptor cells by differential screening with [32P]cDNAs derived from the heads of mutant flies that have reduced amounts of these tissues and cells (Microcephalus, glass3, and sevenless, respectively). Secondly, we identified opsin genes by hybridization with synthetic [32P]oligonucleotides that encode domains that have been conserved between some opsin genes. We found seven clones that contain genes expressed only in the eye or optic lobes of Drosophila; three are expressed only in photoreceptor cells. One is expressed only in R7 photoreceptor cells and hybridizes to some of the previously mentioned oligonucleotides. The complete DNA sequence of the R7-specific opsin gene and its 5' and 3' flanking regions was determined. It is quite different from other known Drosophila opsin genes, in that it is not interrupted by introns and shares only 37-38% amino acid identity with the proteins encoded by these genes. The predicted protein structure contains many characteristics that are common to all rhodopsins, and the sequence differences help to identify four domains of the rhodopsin molecule that have been conserved in evolution.

Amino Acid Sequence↗
PubMed1997

Control of Drosophila retinoid and fatty acid binding glycoprotein expression by retinoids and retinoic acid: northern, western and immunocytochemical analyses.

In Drosophila, thorough retinoid deprivation is possible, optimizing investigation of the effects of vitamin A metabolites and retinoic acid on the visual system. Retinoids had been found to control transcription and translation of Drosophila's opsin gene. To follow this line of inquiry, we examined the effect of retinoids on the translation and transcription of a Drosophila Retinoid and Fatty Acid Binding Glycoprotein. Western blots showed that this protein is high in retinoid replete flies and low in deprived flies. Flies grown on media capable of activating the opsin gene's transcription and which contain alternate transcription activators including retinoic acid yielded extracts containing significant amounts of Retinoid and Fatty Acid Binding Glycoprotein. Immunocytochemistry confirmed its absence in deprived flies and its presence in flies reared or replaced on these diverse media containing retinoids or general nutrients. Immunocytochemistry localized Retinoid and Fatty Acid Binding Glycoprotein to the Semper (cone) cells and the intraommatidial matrix (the interphotoreceptor matrix of the ommatidium). Positive staining of Semper cells in mutants of the opsin gene and a mutant lacking receptors suggests that Retinoid and Fatty Acid Binding Glycoprotein does not depend on presence of opsin and that it is not synthesized in receptor cells respectively. Northern blots demonstrated greatly diminished mRNA for Retinoid and Fatty Acid Binding Glycoprotein in flies grown on deprivation food relative to flies grown on normal food. Although the synthesis of Retinoid and Fatty Acid Binding Glycoprotein does not require chromophore precursors as does that of opsin, the control of Retinoid and Fatty Acid Binding Glycoprotein and opsin transcription by retinoids including retinoic acid might very well be the same. Our results suggest that Retinoid and Fatty Acid Binding Glycoprotein may be involved in retinoid transport. Also, Semper cells may be analogous to vertebrate retinal pigment epithelium in retinoid metabolism and/or delivery.

Animals↗
PubMed2000

The murine cone photoreceptor: a single cone type expresses both S and M opsins with retinal spatial patterning.

Mice express S and M opsins that form visual pigments for the detection of light and visual signaling in cones. Here, we show that S opsin transcription is higher than that of M opsin, which supports ultraviolet (UV) sensitivity greater than midwavelength sensitivity. Surprisingly, most cones coexpress both S and M opsins in a common cone cell type throughout the retina. All cones express M opsin, but the levels are graded from dorsal to ventral. The levels of S opsin are relatively constant. However, in the far dorsal retina, S opsin is repressed stochastically, such that some cones express M opsin only. These observations indicate that two different mechanisms control M and S opsin expression. We suggest that a common cone type is patterned across the retinal surface to produce phenotypic cone subtypes.

Animals↗
PubMed1997

Mutation of a conserved cysteine in the X-linked cone opsins causes color vision deficiencies by disrupting protein folding and stability.

PURPOSE: To test the effects of disruption of a conserved cysteine in the green cone opsin molecule on light-activated isomerization, transducin activation, folding, transport, and protein half-life. METHODS: Stable cell lines were established by transfecting 293-EBNA cells with a plasmid containing wild-type or mutant (C203R, C203S, C126S, C126S/C203S) green opsin cDNA molecules. The proteins were induced by culturing the cells in the presence of cadmium chloride and analyzed by spectra, transducin activation, Western blotting, pulse-labeling with immunoprecipitation, and immunocytochemistry. RESULTS: The C203R mutation disrupts the folding and half-life of the green opsin molecule and its abilities to absorb light at the appropriate wavelength and to activate transducin. Similar disruption of folding, half-life, and light activation occurs when Cys203 or its presumed partner for formation of a disulfide bond (Cys126) is replaced by serine residues. CONCLUSIONS: Like rhodopsin, the folding of the cone opsins appears to be dependent on the formation of a disulfide bond between the third transmembrane helix and the second extracellular loop. Disruption of this disulfide bond represents a cause of color vision deficiencies that is unrelated to spectral shifts of the photopigment.

Amino Acid Sequence↗
PubMed1992

Constitutively active mutants of rhodopsin.

Two critical amino acids in the visual pigment rhodopsin are Lys-296, the site of attachment of retinal to the protein through a protonated Schiff base linkage, and Glu-113, the Schiff base counterion. Mutation of Lys-296 or Glu-113 results in constitutive activation of opsin, as assayed by its ability to activate transducin in the absence of added chromophore. We conclude that opsin is constrained to an inactive conformation by a salt bridge between Lys-296 and Glu-113. Recently, one of the mutants, K296E, was found in a family with retinitis pigmentosa, suggesting that degeneration of the photoreceptor cells in individuals with this mutation may result from persistent stimulation of the phototransduction pathway.

Amino Acid Sequence↗
PubMed2000

Visual pigments of African cichlid fishes: evidence for ultraviolet vision from microspectrophotometry and DNA sequences.

We have found evidence for ultraviolet visual capabilities in a Lake Malawi cichlid fish, Metriaclima zebra. Microspectrophotometry of single cones revealed a visual pigment with peak sensitivity at 368+/-4 nm. M. zebra also expresses a putative ultraviolet opsin gene whose sequence is closely related to the SWS-1 opsin for other fishes. Several other African cichlids have a functional copy of this UV gene in their genomic DNA, but do not appear to express this gene as adults. These results suggest that ultraviolet vision is important for some cichlid fishes. UV wavelengths should therefore be included in future studies of cichlid vision, behavior and color patterns.

Amino Acid Sequence↗
PubMedDate not supplied

Limulus opsins: diurnal regulation of expression.

Much has been learned from studies of Limulus photoreceptors about the role of the circadian clock and light in the removal of photosensitive membrane. However, little is known in this animal about mechanisms regulating photosensitive membrane renewal, including the synthesis of proteins in, and associated with, the photosensitive membrane. To begin to understand renewal, this study examines diurnal changes in the levels of mRNAs encoding opsin, the integral membrane protein component of visual pigment, and the relative roles of light and the circadian clock in producing these changes. We show that at least two distinct opsin genes encoding very similar proteins are expressed in both the lateral and ventral eyes, and that during the day and night in the lateral eye, the average level of mRNA encoding opsinl is consistently higher than that encoding opsin2. Northern blot assays showed further that total opsin mRNA in the lateral eyes of animals maintained under natural illumination increases during the afternoon (9 & 12 h after sunrise) in the light and falls at night in the dark. This diurnal change occurs whether or not the eyes receive input from the circadian clock, but it is eliminated in eyes maintained in the dark. Thus, it is regulated by light and darkness, not by the circadian clock, with light stimulating an increase in opsin mRNA levels. The rise in opsin mRNA levels observed under natural illumination was seasonal; it occurred during the summer but not the spring and fall. However, a significant increase in opsin mRNA levels could be achieved in the fall by exposing lateral eyes to 3 h of natural illumination followed by 9 h of artificial light. The diurnal regulation of opsin mRNA levels contrasts sharply with the circadian regulation of visual arrestin mRNA levels (Battelle et al., 2000). Thus, in Limulus, distinctly different mechanisms regulate the levels of mRNA encoding two proteins critical for the photoresponse.

Animals↗
PubMed1993

Bovine pancreatic trypsin inhibitor-trypsin complex as a detection system for recombinant proteins.

Bovine pancreatic trypsin inhibitor (BPTI) binds to trypsin and anhydrotrypsin (an enzymatically inactive derivative of trypsin) with affinities of 6 x 10(-14) and 1.1 x 10(-13) M, respectively. We have taken advantage of the high affinity and specificity of this binding reaction to develop a protein tagging system in which biotinylated trypsin or biotinylated anhydrotrypsin is used as the reagent to detect recombinant fusion proteins into which BPTI has been inserted. Two proteins, opsin and growth hormone, were used as targets for insertional mutagenesis with BPTI. In each case, both domains of the fusion protein appear to be correctly folded. The fusion proteins can be specifically and efficiently detected by biotinylated trypsin or biotinylated anhydrotrypsin, as demonstrated by staining of transfected cells, protein blotting, affinity purification, and a mobility shift assay in SDS/polyacrylamide gels.

Animals↗
PubMed2000

Pigment epithelium-derived factor supports normal development of photoreceptor neurons and opsin expression after retinal pigment epithelium removal.

Dysfunction of the retinal pigment epithelium (RPE), its loss, or separation from the underlying neural retina results in severe photoreceptor degeneration. Pigment epithelium-derived factor (PEDF) is a glycoprotein with reported neuroprotective and differentiation properties that is secreted in abundance by RPE cells. The "pooling" of PEDF within the interphotoreceptor matrix places this molecule in a prime physical location to affect the underlying neural retina. The purpose of this study was to analyze the morphogenetic activity of PEDF in a model of photoreceptor dysmorphogenesis induced by removal of the RPE. Eyes were dissected from embryonic Xenopus laevis, and the RPE was removed before culturing in medium containing PEDF, PEDF plus anti-PEDF antibodies, or medium alone. Control retinas were maintained with an adherent RPE. Light and electron microscopic analysis was used to examine retinal ultrastructure. Opsin was localized immunocytochemically and quantified as an index of outer segment membranous material and photoreceptor protein expression. Removal of the RPE resulted in an aberrant assembly of photoreceptor outer segments, loss of fine subcellular ultrastructure in photoreceptors, and a reduction in opsin protein levels when compared with control retinas. The addition of PEDF prevented the dysmorphic photoreceptor changes induced by RPE removal. In particular, photoreceptor ultrastructure, outer segment membrane assembly, and steady-state levels of opsin were equivalent to control conditions. Anti-PEDF antibodies completely blocked the morphogenetic activity of PEDF. These results indicate that PEDF is able to mimic the supportive role of the RPE on photoreceptors during the final stages of retinal morphogenesis.

Animals↗
PubMed1988

9,13-dicis-rhodopsin and its one-photon-one-double-bond isomerization.

Incubation of purified 9,13-dicis-retinal with cattle opsin in 2% digitonin at 20 degrees C produced two pigments, one unstable (lambda max 478 nm) and the other stable (lambda max 485 nm) in hydroxylamine. The two pigments exhibited different characteristics. HPLC analysis revealed that the chromophores of these pigments have respectively 9,13-dicis and 9-cis geometries. Under various conditions the amount of 9,13-dicis-rhodopsin formed never exceeded 30% of the total pigments. The addition of 9,13-dicis-retinal to the ROS suspension containing opsin produced 9-cis-rhodopsin in 97% yield. Irradiation of the 9,13-dicis-rhodopsin mainly produced 13-cis-retinal, while 9-cis-rhodopsin produced the all-trans isomer. These results demonstrated that the one-photon-one-double-bond isomerization process took place in 9,13-dicis-rhodopsin.

Animals↗